1. Technical field
The present invention relates to ultrasound imaging devices for medical diagnostics and in particular to a hand held apparatus for producing two-dimensional and three-dimensional images of structures within a patient's body such as organs and blood vessels.
2. Background Information
It is well know to use sound waves in the two to ten megahertz range for producing images of internal structures, especially of a medical patient's organs. A device transmits a sound wave, receives, and processes reflected sound wave energy to produce an image. Such devices may use one transducer or a plurality of transducers arranged in an array. A transducer can either transmit a signal, receive a signal, or perform both tasks. As sound waves produced by one or more transducers travel through soft tissue some of the sound waves are reflected back toward the source. A receiver(s) senses this sound energy and creates a signal that can be electronically translated into a viewable image, usually on a monitor.
Devices of this type for use in the medical field are generally referred to as ultrasound systems. Modern ultrasound systems generally use a plurality of transducers arranged in a linear or circular array. By suitably adjusting the phase on each transducer, sound energy is focused on a small region of an object being imaged. This focusing procedure is generally referred to as beam forming. In the receive mode, transducers can also be phased to receive energy from a selected region within the object being imaged. By repeating this process a high resolution image of the object is obtained by adding all of the individual images together.
Since ultrasound systems are so useful as a diagnostic tool, there is a great need to provide a simple to use and relatively inexpensive device for imaging internal human structures. The device needs to be small enough to be hand held and have reasonably small power requirements. This type of device would be invaluable in a clinic or doctor's office setting where larger and/or more expensive devices are not feasible. The bulk, weight and size of ultrasound systems results from the amount of electronics needed to perform beam-forming operations. Developmental efforts are being directed at the design of specialized micro-chips to perform the beam forming operations. It is hoped that incorporation of these micro-chips will reduce the over all weight and size of the systems.
An alternative approach is to avoid the use of an array by using a single transducer that acts as both a transmitter and receiver, referred to as mono-static. These transducers are shaped to focus sound. In order to image an object, the transducer is rotated mechanically by a stepper motor or the like. The echo signals are arranged to give an image of the object. The disadvantages of this approach are the limitations on resolution imposed by the depth of focus of the transducer and the scanning rate, and the power requirements for a mechanical sector scanner. These devices only produce two-dimensional images. The present invention solves these problems by improving the image quality, or resolution, and by using less power, thereby prolonging battery life which reduces the cost of the device.
It is also known to use a two-dimensional receiver matrix to produce a three-dimensional image. A limiting factor on the design of systems for three-dimensional imaging is the required resolution of the resulting images. Current systems use a phased array scheme to form a scan beam and to receive the signal reflected by the structures to be imaged. Three-dimensional systems currently use planar arrays. Systems can vary by the number of elements in an array and are directly related to the image resolution. In a system having an array of 64.times.64 elements the total number of elements is 4, 096. The electronics associated with the phasing of this number of elements requires increased size, weight, and cost of the system. The medical field would greatly benefit from a device that alleviates the foregoing problems. The currently available hand held systems do not provide three-dimensional imaging.
The present invention does not require any mechanical scanning or the electronics for beam-forming operations. The scan beams are formed simultaneously through the use of a curved reflector, thereby reducing the time required to produce an image. This also reduces the power consumption of the unit, which in turn reduces the size and weight of a battery pack. The scan beams of the present invention can be focused both in a transmit mode and receive mode by selection of a suitably shaped acoustic reflector (lens). This provides increased resolution without penalty of greater size or weight. By utilizing a two-dimensional array of signal receivers a three-dimensional image is possible. Scan beam forming of the present invention is done with inexpensive components compared to phased array systems making it a breakthrough development in three-dimensional imaging and hand-held devices.